when i did it a few years agao i had issues, they never todl me till about 5th tech to power off iphone for 2 minutes then power on then when pressed VM button it dialed my rogers mailbox and entered my new password ( by default when swithing is usally last 4 digits of you phone # )
The voicemail password can be changed by logging into your My Rogers account. You don't have to know the previous password in order to change it. The "Update voicemail password" option appears in the Wireless section on the Overview tab.
Displaying the keypad in the phone app and holding "1" until voicemail is dialed is a useful technique when roaming, as Visual Voicemail requires cellular data in order to function.